1. Field of the Invention:
The present invention relates to dielectric ceramic compositions allowing low-temperature sintering, and exhibiting high dielectric constant, and being suitable for use in multilayer ceramic capacitors.
2. Description of the Prior Art:
As promising ceramic compositions for this application, ceramic compositions essentially consisting of BaTiO.sub.3 have been widely used as a materials of high dielectric constant. However, the BaTiO.sub.3 system ceramics must be sintered at a very high temperature in the range of 1300.degree. C. to 1400.degree. C., so that where they are used as a dielectric material of multilayer ceramic capacitors, expensive metals such as platinum or palladium which can stand such high sintering temperature should be used as internal electrodes of the capacitors. Therefore there has still been a demand for dielectric ceramic materials which can be sintered at a temperature as low as below 1000.degree. C. for enabling the use of relatively cheap metal such as silver for the internal electrodes.
U.S. Pat. No. 4,078,938 has described binary system ceramic compositions of PbFe.sub.2/3 W.sub.1/3 O.sub.3 --PbFe.sub.178 Nb.sub.1/2 O.sub.3 which can be sintered at a relatively low temperature, and which exhibit high dielectric constant. However, the ceramics have low specific resistance.
U.S. Pat. No. 4,236,928 has described binary system ceramic compositions of Pb(Fe.sub.2/3 W.sub.1/3)O.sub.3 --Pb(Zn.sub.1/3 Nb.sub.2/3)O.sub.3 which can be sintered at a temperature below 1000.degree. C. However, the ceramics have relatively low dielectric constant.